Monitoring airborne particles is of concern in a number of civilian and military contexts. Airborne hazards can come in a variety of forms, for example, of biological, chemical, or radiological nature. Sometimes severe biological airborne perils may suddenly arise at unpredictable locations, such as in bio-terrorist attacks. The most efficient response to biohazards can be mounted based on their earliest practicable detection.
The typical problem facing the aerosol field is that of collecting and characterizing airborne particles. Characterization of these airborne particles can be performed in situ (i.e., while the particles remain suspended in a gas), or in extractive techniques where particles are collected and then deposited onto a solid substrate or into a liquid for the purpose of subsequent physical or chemical analysis.
Identifying biological materials in situ has been attempted by detection of autofluorescence of airborne bacteria. While autofluorescent properties may be useful in detecting biological particles, their in situ measurement is challenging for a number of reasons. It is particularly difficult to measure fluorescent characteristics of minuscule particles in an airborne state. The particles are available for analysis quite briefly, thus making it difficult to determine several informative characteristics. In addition, the equipment required comprises expensive powerful lasers and sensitive fluorescence photodetectors or photon counters. The resulting devices are large and expensive, making this technology unlikely to be adopted for some applications, such as routine monitoring of civilian buildings.
In alternative approaches, extractive instruments such as jet impingers, jet impactors, cyclones, and filters deposit particles onto substrates, which may be liquids, surfaces such as greased slides or agar-coated plates, or filters. The content of extracted particles can then be analyzed by any desirable technique. While analysis of airborne particles may be performed more thoroughly with extractive rather than in situ techniques, extractive techniques require consumables such as deposit substrates and/or analysis reagents and/or human involvement in the analysis. Continuous use of consumables and/or labor can become problematical and prohibitively expensive. Therefore, monitoring systems based on extractive techniques are also of questionable value for routine, continuous use.
There is a current need for devices and methods to continuously detect airborne particles. Continuous monitoring of the largest possible number of populated premises seems the most desirable option in dealing with the unpredictability of airborne biohazards emergence. Widespread adoption of such devices would allow protection of a large number of potentially endangered persons. For widespread adoption, however, such devices should be fairly inexpensive and reliable. Operation of the device should be automatic, i.e. not requiring any user input. In addition, to be used routinely in a large number of buildings airborne biohazard detection devices should ideally be maintenance free and use no consumables.